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Lesson Content

Testing JavaScript Code

Testing ensures your code works correctly and prevents bugs. Learn to write effective tests for JavaScript applications.

Unit Testing

// Simple test function
function test(description, fn) {
  try {
    fn();
    console.log('✓', description);
  } catch (error) {
    console.log('✗', description);
    console.error(error);
  }
}

function expect(actual) {
  return {
    toBe: (expected) => {
      if (actual !== expected) {
        throw new Error(`Expected ${expected}, got ${actual}`);
      }
    }
  };
}

Test Structure

// Arrange - Set up test data
// Act - Execute code
// Assert - Verify results

Testing Async Code

async function testAsync() {
  const result = await asyncFunction();
  expect(result).toBe(expected);
}

Example Code

Write tests for JavaScript functions

// Simple test framework
function test(description, fn) {
  try {
    fn();
    console.log('✓', description);
  } catch (error) {
    console.log('✗', description);
    console.error(error.message);
  }
}

function expect(actual) {
  return {
    toBe: (expected) => {
      if (actual !== expected) {
        throw new Error(`Expected ${expected}, got ${actual}`);
      }
    },
    toEqual: (expected) => {
      if (JSON.stringify(actual) !== JSON.stringify(expected)) {
        throw new Error(`Expected ${JSON.stringify(expected)}, got ${JSON.stringify(actual)}`);
      }
    }
  };
}

// Function to test
function add(a, b) {
  return a + b;
}

// Tests
test('adds 2 + 3 to equal 5', () => {
  expect(add(2, 3)).toBe(5);
});

test('adds negative numbers', () => {
  expect(add(-1, -2)).toBe(-3);
});

Expected Output:

✓ adds 2 + 3 to equal 5
✓ adds negative numbers

Study Tips

•Read the theory content thoroughly before practicing
•Review the example code to understand key concepts
•Proceed to the Practice tab when you're ready to code